Expanded knowledge and clinical application of the optical properties of natural teeth, skin, dental and maxillofacial materials are necessary as a long-range goal for improved color replication involving both intra- and extra-oral restorative procedures. Patients needing restorative dental treatment and/or facial prosthetic reconstruction can experience improved quality of life with the advancement of the dental color replication process. By applying established psychophysical methodology, the following specific aims target improving the accuracy of the color replication process for dentistry: (1) To determine the color difference formula that provides the best indicator for perceptibility and acceptability of small color differences by human observers and (2) To determine the difference and magnitude of perceptible and acceptable color differences within the color range of human dentition. Methods: Anterior tooth color measurements will be taken from 50 subjects to determine the range of color of human dentition (Experiment I). This information will be used to plan color differences between standard "tooth" and comparison "restoration" pairs (Phases I, II, III of Experiment II). Three different sets of 24 subjects will be recruited, one for each phase. The subject population consists of four observer groups: dentists, auxiliaries, technicians and patients. Subjects will evaluate perceivable and acceptable color differences among the tooth/restoration pairs that are presented (1) as disks fabricated with opaque porcelain - Phase I, (2) as disk models on a computer screen - Phase II, or (3) as three-dimensional adjacent "tooth" and "crown" models on a computer face model - Phase III. From our preliminary study, the proposed distribution of the color difference between standard and comparisons are 0,0.5,1, 1.5, 3, 4.5 delta Es. The magnitude of the color difference will be due to variations according to either a change in direction of L*a* or b*. Statistical analyses: The receiver operator characteristics curve (ROC) will be generated for each subject's data and the various color difference formulas for perceptibility and acceptability. The area under the curves will be calculated and ranked. The optimal factor for the CMC color difference formula will be determined using designed experimental sets. A repeated measures analysis of variance (alpha= 0.05) will be applied to determine statistical significance of fit among the observer groups; the CIELAB color difference formula and the optimal CMC color difference formula for both perceptibility and acceptability. The 50:50 delta E point for perceptibility and acceptability will be determined for each observer group and each formula. Tukey's Studentized Range Test (alpha=O.05) will be used as a post hoc test. A chi-square test will compare data from phase I and II to assess validation of the computer with the actual sample model.